Transplants of cells and tissue engineered organs and tissues offer promise in facilitating tissue healing and repair and the replacement or treatment of diseased or dysfunctional organs. According to data from the American Association of Tissue Banks (AATB), a voluntary accreditation organization that sets standards for tissue banking, approximately 1.5 million bone and tissue allografts are distributed each year by AATB-accredited tissue banks in the United States. In the U.S., around 20,000 organ transplants are performed yearly, and the list of individuals in need of tissue and organ transplants is even increasing.
A primary challenge in the transplantation of tissues, organs, cells or an artificially created engineered tissue constructs is ensuring sufficient blood supply to the constituent cells. In the absence of pre-existing vessels in the transplant capable of inosculation with the recipient blood supply, the amount of tissue that can be transplanted is limited by oxygen diffusion.
Ultimately, healthy transplants depend on sufficient vessel density within the transplanted tissue or organ and the organization of the vessels into a network comprised of low-resistance conduit vessels (arteries), a functional microcirculation (arterioles and capillaries) for a proper blood-tissue exchange, and drainage/compliance vessels (venules and veins).
Existing strategies for building a vascular system for tissue engineered constructs have been based on using cultured, human endothelial cells. For example, reparation of pre-formed vascular beds to be incorporated in the tissue, organ or cell transplant interface at the time of transplantation have been described in U.S. Pat. No. 7,052,829. However, growing such constructs is labor intensive and takes time which is not available specifically, when transplanting donated tissues, organs and cells, wherein the transplantation typically must occur within hours of removal of the organ, tissue or cell from a donor.
Currently, organs such as heart, kidneys, liver, lungs, pancreas, and intestines, can be transplanted as whole organs. Many classifications of tissue may also be transplanted including whole eyes or corneas, heart valves, cardiovascular tissue, which includes the thoracic aorta, the abdominal aorta with iliac arteries, saphenous veins, and femoral vessels, may be donated to restore compromised blood circulation. Bone and soft musculoskeletal tissue, such as ligaments, are also suitable for transplantation for orthopedic and spinal surgeries and sports medicine injuries. Skin can be transplanted to promote healing and prevent infection in critically burned individuals.
Accordingly, improved methods for increasing vascularization of transplants such as donated and engineered tissues, cells and organs are needed.